This invention relates to ignition and control systems for gas burning apparatus and more particularly to an improved ignition and control system for the reliable and safe operation of gas burning apparatus of the type in which a pilot flame is established each time operation of the gas burning apparatus is required for igniting gas supplied to a main burner.
In some types of gas burning apparatus, it has been a common practice to employ a continuously burning pilot flame for igniting the main burner. To obviate the need for such a gas-wasting operation of a pilot burner, various automatic ignition and control systems have been proposed for directly igniting the main burner of gas burning apparatus with electric ignition means whenever operation of the apparatus is required. Ignition and control systems of this type are the subject of many prior U.S. patents including the following;
U.s. pat. No. 3,384,439, Walbridge -- May 21, 1968 PA1 U.s. pat. No. 3,610,789, Jones -- Oct. 5, 1971 PA1 U.s. pat. No. 3,610,790, Lindberg -- Oct. 5, 1971 PA1 U.s. pat. No. 3,619,097, Clay et al. -- Nov. 9, 1971 PA1 U.s. pat. No. 3,673,464, Lamb et al. -- June 27, 1972 PA1 U.s. pat. No. 3,758,260, Newport et al. -- Sept. 11, 1973 PA1 U.s. pat. No. 3,941,553, Bedford -- Mar. 2, 1976 PA1 U.s. pat. No. 2,981,324, Deziel -- Apr. 25, 1961 PA1 U.s. pat. No. 3,727,073, Cade -- Apr. 10, 1973 PA1 U.s. pat. No. 3,918,881, Matthews -- Nov. 11, 1975
A problem encountered in use of such prior ignition and control systems with high rate gas burning apparatus was the dangerous accumulation of unburned gas in the combustion chamber in the event of failure of the ignition means to promptly ignite gas issuing from the main burner, even when the ignition trial period was limited to a short interval of time by a safety time delay device. To avoid this problem, still other automatic ignition and control systems have been proposed for first igniting a low energy pilot burner with electric ignition means whenever operation for the gas burning apparatus is required and subsequently supplying gas to a main burner for ignition by the pilot burner when the presence of flame at the pilot burner is sensed by flame detecting means. Ignition and control systems of the latter type are disclosed, for instance, by the following U.S. patents:
Many of these prior art ignition and control systems employ flame detecting means comprising a flame sensing electrode positioned adjacent a burner and connected to a solid state flame detector circuit in an attempt to obtain improved safety and reliability. Although some of these systems are designed to prevent unsafe operation of a gas burning apparatus upon a malfunction of certain components of the flame detecting means, none affords complete self-testing of all critical components of the system including the actuator means of the safety time delay device before any gas is allowed to flow. Such a self-checking function is important in preventing operation of a gas burning apparatus when the ignition and control system is incapable of functioning properly to protect against potentially dangerous conditions.